I am a cheat because I don't really
buy books for personal use anymore. I work as a book buyer, so I often get advanced copies of books and get to read those. Plus I can take any book I want from our stock to review it, or to read it.
How I buy books for sale though is kind of different.
1) My boss tells me to!
2) I go through the catalogs and other promotional material I am given.
3) I see a niche and order for it.
4) Someone suggests it.
Usually it is very hit or miss with my store. Some books I cannot BELIEVE people haven't purchased, and other it amazing me when can't keep it in stock. I am considered a book snob though.